WASHINGTON -- Senator Charles Schumer, Democrat of New York, the most senior Jewish member of the United States Congress and likely the next Democratic leader of the Senate, will oppose the Iran nuclear deal reached last month.His declaration in opposition is the first from the Senate Democratic caucus. It is considered influential by his peers: A plurality of Democrats remain undeclared on a pending vote of disapproval over the Joint Comprehensive Plan of Action, while 15 members of the Senate have declared their support.The JCPOA, the formal name for the Iran nuclear accord, is intended to cap, restrict, monitor and partially roll back Iran's nuclear program for a finite period in exchange for sanctions relief. Skeptics of the deal fear it will legitimize Iran as a nuclear threshold state, allowing them to retain an ever-growing uranium enrichment program. "I have decided I must oppose the agreement and will vote yes on a motion of disapproval," Schumer said in a statement. "The agreement would allow Iran, after ten to fifteen years, to be a nuclear threshold state with the blessing of the world community.""To me," he added, "the very real risk that Iran will not moderate and will, instead, use the agreement to pursue its nefarious goals is too great."The move is a challenge to US President Barack Obama, who is aggressively advocating for the agreement. His colleague from New York, Senator Kirsten Gillibrand, announced her intentions to vote in favor of the deal earlier on Thursday.Also this evening, Congressman Eliot Engel (D-New York), ranking member of the House Foreign Affairs Committee and a senior Jewish member, also declared his opposition to the agreement. "The answers I've received simply don't convince me that this deal will keep a nuclear weapon out of Iran's hands, and may in fact strengthen Iran's position as a destabilizing and destructive influence across the Middle East," Engel said.He joins four other Democratic lawmakers from New York that are opposed.